Method of depositing copper



Patented Dec. 29, 1953 2,664,363 Manson oFnEPosITINGcoPPER Max Meth Atlantic City, Nil-. No Drawing. Applicationfiarcli ili l fi} directed, it is to beunder'stood that'the method is not to be restricted thereto and that there is a' broader application. This method maybe-used whenever it'is desired to deposit a layer of copper ornon-conductin'g surface-or For example, in the plating of certain metallic bases with chromium, nickel, sil'ver'or the like by standard electroplating methods? it is often very dificul't to prevent undesirable -oxi-' dization or" the base surface'after" cleaning and before it can be immersed in the bathor before the relatively slow electro-deposition establishes" a protecting layer. This includes attack by oxygen in the air or active chemical ions in-theelectrolyte, and this oxidation causes scaling, peeling and other imperfectionsin the-finished plating. B'y'the present method a layer of free cop-= per may be quickly applied tothe freshly cleaned base surface before oxidization sets inand the surface then electroplated with the stable finish metals such as chrome, nickel or the like;

In the manufactureof si-lvered mirrors'it has" been the standard practice to place the-traine on a perfectly horizontal surface" and then pour a mirroring'solution over thetopsurface of thesheets. prises a silver salt such as silver nitrate (AgNGs) or a complex silver salt such as silver ammonium nitrate (AeNO3NI-I4Os) which has freshly mixed therewith a reducing agent such as Rochelle salt (KNaCrI-hOe-l-lzO), a sugar, formaldehyde (ECHO) or the like. in athin layer of free metal to form the reflecting surface. $ome processes have adopted a method of spraying the silvering solution-on the plate, the silver salt and reducing agentbeing mixed and sprayed on thesurface. The silver layer must then be washed and dried and "the mirror handled and manipulated" to transfer it to a copper electroplating bath, where there flective coating becomes an electrode and has deposited thereon a protective layer of copper. The copper layer is then covered by spraying, brushing or rolling with a paint well known to the industry.

The handling of the freshly silvered mirror The solution usually com---- i The silver is precipitated without injury" to the thin reflective" surface he: comes a: serious practical problem. The" layer is easily scratched and rubbed oiT, and the sup porting of the'plate in the'bath and establishment of electrical connections difiicult, time d costly. It ha also been found that in theelectroplatin'g" there is some reaction between the-layers of silver and copper, with" a seriousimpairment in" the'qua-lity of the'niirror.

In using the electroplating" processes; due" to the difiiculties' just mentioned-,3 manufacturers nowexperience a-reject 1o s-or-from-5%- to 20 of the total volume '"andthere Still anotherobject' the invention is to" pro vide a wherever and'without the'use' of spe- A further object of the invention'is to provide a method of applying a protective copper'coatm to the silverecrsurrace oftheiniribrwhich eliminates costlyel'ec'troplatingjsteps; reduces the percentage of rejets to' a negligible 'amcunt', and silver and copper prevents reactions" between coatings which impair thequality of the mirror;

will be presently apparent, the invention consists in general of certain novel details hereinafter fully described and particularly claimed.

In carrying out the present method any known process for depositing the silver reflective coating may be used. The transparent plate may be placed horizontally and the flow method used, but in connection with the present disclosure it is preferable that the spray method be used and the plates racked up substantially vertical or at a sharply acute angle to the vertical.

A tank is provided containing a water solution of copper sulfate (CllSOe), which tank is substantially above the level of the work to establish flow, and is provided with a lower outlet aperture. A second tank is also used, which tank contains a very finely divided metallic zinc or zinc dust suspended in water. It is highly necessary and a very important part of the present improved method that this suspension be kept violently agitated. Any desired means may be used to maintain a homogeneous suspension, such as compressed air or vibration of the container, but agitation by a motor driven screw or paddles has been found to be most efficient.

Hoses or conduits are used to conduct the solution and suspension from the tanks to a mixing nozzle. In the preferred method, compressed air is supplied to the nozzle and the three fluids simultaneously mixed and sprayed upon the silvered reflective surface. The compressed air is not necessary to the method, however, and the pressure head of the solution and suspension may be used to form the spray, or the two solutions may simply be merged and flowed over the silvered surface. It may be noted that the use of compressed air has been found more effective since the air tends to maintain the violent agitation of the zinc particles within the mixing nozzle which gives a more efficient reaction.

Upon the mingling of the CuSOi solution and the zinc suspension, the more active metallic zinc tends to combine with the sulfate (50;) radical and free metallic copper is immediately deposited. The substantially simultaneous mixing of the solution and suspension and application to the reflective surface insures that the metallic copper will be deposited in a firmly adhering coat at the maximum rate and without loss of efficiency due to partial reaction and deposition in a mixing chamber. The homogeneous zinc suspension, due to violent agitation, provides maximum reaction efficiency and an even coating of the free copper, and is absolutely necessary to the practical success of the method.

The method is not necessarily limited to the use of zinc dust and finely divided iron has been found satisfactory as well as certain other commercially available metals above copper in the Activity Series. However, it has been found in actual practice that the use of zinc dust has produced the most efficient results.

In carrying out the method, each of the conduits leading from the copper sulfate solution, the zinc suspension and the compressed air supply are appropriately valved and the relative rate of supply of the fluids is carefully and critically controlled so as to properly form the deposit, and the nozzle is provided with a lever operated master valve so that the operator may cut the spray on or off at will.

In extensive tests with this method it has been found that a copper sulfate solution having a proportion of 16 ounces CuSO4 to the gallon of water and a zinc suspension of 3.2 ounces Zn to the gallon of water is to be preferred and gives a coating of maximum quality. It has been found possible, however, to vary the strength of the solution in the proportion of 6 to 40 ounces per gallon of water and to vary the density of the suspension in the range of 1 to 6 ounces of zinc dust per gallon of water.

It has been found that the copper layer doposited by this method completely seals and protects the silver reflecting layer and that there is no interaction between the coats which might spot or impair the reflecting quality of the mirror.

While there is herein shown and described the preferred embodiments of the invention, it is nevertheless to be understood that minor changes may be made therein without departing from the spirit and scope of the invention as claimed.

What is claimed is:

1. The method of producing a copper plated silvered mirror including the steps of mounting a transparent plate on a supporting rack, chemically depositing a silver reflective coating from a silver depositing solution on said plate while in its mounted position, and then while the silver reflecting surface is still wet and the plate in place on the rack simultaneously intermingling and spraying onto said surface a copper sulfate solution and a substantially homogeneous fluid suspension of finely divided zinc dust to thereby deposit a copper protective layer.

2. The method of producing a copper plated silvered mirror including the steps of mounting a transparent plate on a supporting rack, chemically depositing a silver reflecting coating from a silver depositing solution on said plate while in its mounted position, and then while the silver reflecting surface is still wet and the plate in place on the rack simultaneously intermingling and spraying onto said surface a solution of cop per sulfate and a mixture of zinc dust and Water, said zinc dust being maintained in homogeneous fluid suspension in the water by the continuous and vigorous agitation of the mixture supply.

3. The method of producing an article having a copper plated silvered surface including the steps of mounting the silver surfaced article on a support, simultaneously intermingling and applying to said surface a stream of copper sulfate solution with a fluid stream composed of a mix ture of water and finely divided zinc dust while on said support, said water and zinc dust being maintained in substantially homogeneous suspension by the continuous and vigorous agitation of the supply of said mixture.

MAX METH.

References Cited in the file of this patent UNITED STATES PATENTS 

1. THE METHOD OF PRODUCING A COPPER PLATED SILVERED MIRROR INCLUDING THE STEPS OF MOUNTING A TRANSPARENT PLATE AS A SUPPORTING RACK, CHEMICALLY DEPOSITING A SILVER REFLECTIVE COATING FROM A SILVER DEPOSITING SOLUTION ON SAID PLATE WHILE IN ITS MOUNTED POSITION, AND THEN WHILE THE SILVER REFLECTING SURFACE IS STILL WET AND THE PLATE IN PLACE ON THE RACK SIMULTANEOUSLY INTERMINGLING AND SPRAYING ONTO SAID SURFACE A COPPER SULFATE SOLUTION AND A SUBSTANTIALLY HOMOGENEOUS FLUID SUSPENSION OF FINELY DIVIDED ZINC DUST TO THEREBY DEPOSIT A COPPER PROTECTIVE LAYER. 